Hi Tony, Really good presentation - I like it!
I have made lots of ceramic and other burners. - I sold more than a dozen assorted burners on £&@y a couple of years ago as I just had more than enough kicking around.
I have been interested in these burners since to mid-1990s when I made my first ceramic. it still works, though have tried to tune it to get it cleaner and failed! My Father had made a half-dozen or more burners for a 3 inch bench horizontal boiler- pressurised paraffin blowlamp style, or flat quiet burners. But that first ceramic is still a good burner for the boiler. But I have now made a larger burner - as on the bench I can use a lot of steam with various engines.
A couple of points, most come from Industry (and a bit of Physics!) - which you probably know, but of which some readers of your thread may not be aware.
Simply. Gas (fuel) power is everything in a boiler. For the same jet and air system the burner is of a fixed size, so the heat from it is in 2 useful forms: Hot gases and radiant heat. So performance of these burners being "nearly the same" is not unexpected if the boiler is efficiently gathering as much heat as it can. So the Combination of "optimum burner and boiler" usually is the one that gives best results on that boiler.
But here are the "limiting factors" that affect burners in enclosed spaces - such as a firebox.
- Jet and air intake.
- The correct jet size for the air intake will burn all the gas cleanly, and not heat "excess air" which wastes heat by taking "hot air" up the exhaust stack. (=Too much air and air drawn-in other than through the air-intake holes).
- Too little air makes CO - which is a toxic gas and has no smell but can be detected easily by domestic CO detectors that cost just a few £. - Well worth getting one! - I can set mine off when I use and enclosed space (garage with door only slightly ajar) and the burner air intake is to small for the jet! (shows as "top-flame" on a ceramic).
- The temperature of the ceramic can get too high - when "by eye" it starts to get more yellow than Orange it is starting to get too hot - If the ceramic gets to hot the underside gets to ignition temperature an the gas than ignites below the ceramic - DANGEROUS combustion that can produce higher levels of CO gas, and melt or otherwise destroy burners. I have cracked burners which have simply crumbled on cooling because I tuned them to see how hot they could take (Yellow heat!). Manufacturers of ceramic burners use 900deg.C MAX. (mid-orange heat).
- The boiler "restriction" through the flue can limit the amount of exhaust gas that the boiler can pass. At the limit the burner makes flames that start to come out of any gaps (a lighting hole, or whatever?) - and before that the burner will limit the air intake from back-pressure - so it makes CO gas in the exhaust!
- Adding a shield above a ceramic heats the ceramic to a higher temperature, and the heat is mostly lost by radiation, so in the should design that and burning gas are heating the shield - which is simply radiating the heat to the boiler instead of the ceramic radiating that heat directly - and at a hotter temperature and more efficient heat transfer (Physics). So a solid shield is no good on a radiant burner below. It does work as an effective radiant for JUST blue flames below. But Wire-mesh is very effective (an extra 10% radiant heat according to "industry" instead of a solid shield.
- The boiler cannot capture radiant heat where it shines straight through the flue tube. But if many cross-tubes block the view of the ceramic by "eye" they will be capturing that heat.
- Firebox side-walls will take radiant heat that shines on the side walls, and loose it to the outside as waste, or, if containing water, will heat the water. A shiny inside - such as a stainless steel liner - will reflect 90% of the heat for absorption elsewhere.
- Similarly, a "black-bottomed" boiler will accept more radiant heat than any other colour. Pickled copper is only half as good as "black" copper for absorbing that radiant heat.
- After watching the video, and from my own experience and gathered knowledge, the stainless wire-mesh burners - providing they do not flash-back - are simply the best, as they can withstand higher temperature. Which gives better radiant heat transfer.
- The stainless deflectors do nothing to improve radiant heat transfer to the boiler, they simply convert more efficient (hotter) radiant from the ceramic into less efficient (cooler) radiant from the stainless deflector (a duller red). However, they do flatten the flame and improve combustion, which may give hotter exhaust gas and improve hot-gas to boiler heat transfer. I suspect that timing the laps may give a more accurate indication of any real improvement for the particular burner and boiler combination. The objective being to maximise the sum of radiant + gas conduction heat transfer from the burnt gas to boiler. A wire mesh dome is an accepted industrial way to improve radiant heat transfer (10% more radiant = 10% less hot gas).
- An example: A burner, burning gas with 1000W of chemical energy, can heat the boiler in 2 ways. Hot gas passing through, and heat transfer by conduction with boiler surfaces. and by radiant heat shining on the metal surfaces of the boiler. If the burner has "no radiant", it acts like the gas is a "cool" radiant at about half or less of the heat transfer power of a ceramic or S/S surface. So maybe 10% of heat is transferred by radiant heat from flames? Another 10% or 15% of heat is transferred by radiant heat if there is a "red-hot" surface... - A bed of hot coal when a coal fired boiler is working hard can give 25% or more of its heat as radiant to the inside of the firebox, because it is so much hotter than a ceramic can be. Yellow flames also transmit a lot of radiant heat, while wasting a lot of unburnt fuel up the chimney! (more than half is wasted?). The remainder of the burnt gas transfers heat to hot walls of the boiler, and superheater, but cannot transfer any heat to surfaces below the boiler temperature. SO 10~15% of the heat leaves the boiler up the flue!
- This means: "no radiant": ~10% radiant heat from flames, + 75% of heat from gas-copper conduction and 15% hot exhaust from the flue? = 850W transferred to steam and losses from the unlagged surfaces around the outside.
- Or with a radiant surface: 25% radiant heat from ceramic + 10% radiant heat from flames, + 55% of heat from gas-copper conduction and 10% hot exhaust from the flue? = 900W transferred to steam and losses from the unlagged surfaces around the outside. - I.E. about 5% more efficient?
- But if the boiler cannot extract all the heat from the flue gasses, because of a lack of boiler surface area, (like the simple single flue boiler) then maybe another 20% or more of the "flame heat" goes "up the flue" and is wasted, reducing boiler efficiency very significantly. - A chip-pan thermometer can be used (carefully) to determine the flue gas temperature...
These are CRUDE (Guessed!) values, but may help to explain why it is difficult to make judgements of the efficacy of ceramic or S/S radiant burners...
What is important is the CORRECT tuning of gas and air (No detectable CO), then confirmation that the back-pressure inside the firebox is not making that "NG" (Poisonous with CO gas production!). - I use the domestic CO alarm to make sure even the best-looking burner in a firebox is good. - But it is deafening when there is CO present! = Ouch! You may be surprised at the difference between a burner "in air" and "in boiler" when tested with a CO alarm... - or "not" if your system is Good! (I suspect it is good.).
Keep up the excellent presentations. Good work! (Better than some books I have bought!).
K2
